1. Field of the Invention
The present invention relates to a process for the production of sulfone polymer foams, and more particularly to a process employing aqueous blowing agents for the production of low density polysulfone, polyarylsulfone and polyethersulfone foams, and foams of blends of sulfone polymers with other foamable polymers.
2. Description of the Related Art
Sulfone polymeric materials are known for their useful characteristics as engineering thermoplastics for high temperature applications. Foams from these materials have been made with difficulty since the high temperatures necessary to produce a flowable gel from sulfone polymeric materials causes problems with the usual blowing agents.
One approach to the manufacture of polysulfone foams has been to use volatile organic solvents such as methylene chloride to form flowable compositions which can be foamed. U.S. Pat. No. 4,308,352 discloses a method using this and related organic liquids as solvents and plasticizers and, ultimately, as blowing agents for the manufacture of polysulfone foams.
Another problem in the art associated with solvent type blowing agents is adhesion to various substrates, including those of the processing equipment. The use of various solvents improves mold fill, but this aggravates the adhesion problem. An approach to this problem is disclosed in U.S. Pat. No. 4,1798,540, which employed a very small amount of water in conjunction with a blend of various resins, including polysulfones, and normally liquid organic solvents to form a non-tacky hydrogel dough.
All processes for the production of foams which employ CFC's and related halogenated solvents and blowing agents are under scrutiny today in hopes that the halogenated materials used therein can be eliminated, reduced, or replaced by other materials with lesser environmental impact.
Therefore, it is an objective of the present invention to provide an improved process for the production of foams of sulfone polymers which overcomes the processing problems mentioned above, including high temperature.
Another objective of the present invention is to lessen the environmental impact of the manufacture of sulfone polymer foams through the use of blowing agents with reduced or zero halogen content.